The Centers for Disease Control and Prevention, which regularly tracks telephone usage, says the number of U.S. households relying only on cellular devices for phone service jumped to more than 35 percent by the first half of 2012 from about 20 percent in 2008. But some telecommunications experts warn older people to put plans to drop their landlines on hold.

"Having a quick and reliable option to reach emergency responders and immediate family is essential," says Raghu Santanam, a paramedic and professor of information systems at Arizona State University in Phoenix.

Susan Odom of Atmore, Ala., believes she would have choked to death if she hadn't dialed 911 on a traditional copper wire landline. A 911 call from a cellular phone or an Internet-based Voice over Internet Protocol (VoIP) service often requires routing the call to the correct emergency response center, which can cause delays for first responders when every second counts.

"If you call 911 from a landline, you get several advantages," Odom said on her local newspaper's website of the 2009 incident. "First, the call shows up on a computer screen in the correct 911 center. The screen shows a map and exactly where the call is coming from, the address and the name of the residence. Should the caller be unable to speak, get confused or not know where they are, the 911 screen shows EMS … right where to go."

While "tech-savvy seniors can save money by switching to mobile and Internet-based services," Santanam says, he recommends keeping a landline as a plan B: "It's important to gauge the age-related changes and the convenience of keeping things simple. Given that all seniors are most familiar with landlines, it should be either the first option or the emergency backup option."

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Since copper lines are self-powered, "it makes even more sense," for older people in rural communities or areas prone to storms to resist offers from cable, cellular and satellite companies, Santanam says. "In case of bad-weather conditions, landline phones are much more likely to be available," he says. "For example, satellite-based Internet services in rural areas can have outages during storms." And cellular towers can be vulnerable to losing power in natural disasters, as occurred during Hurricane Sandy.

"If they don't have enough backup battery power for these towers, your cell services will disappear," says Barbara Cherry, a professor in the telecommunications department at Indiana University and a former senior counsel at the Federal Communications Commission's Office of Strategic Planning & Policy Analysis.